The present invention relates to a system of data transmission, particularly one suitable for digital remote control using infrared rays.
A remote control system such as one used in home appliances comprises, as shown in FIG. 1, a transmitter circuit 31, and a light emitting element such as a light emitting diode 33 which are provided in a remote controller and a photo detector such as a photo diode 34 and receiver circuit 32 which are provided in the main part (operative part) of the appliance such a TV set, a VTR, or an air conditioner.
The information or command inputted by mainipulation of keys, not shown, on the remote controller is coded and modulated in the transmitter circuit 31 and is converted at the light emitting element 33 into optical signals, which are propagated typically through the air. The transmitted optical signals are received by the photo detector 34 and converted into electrical signals, which are then demodulated and decoded.
The system shown in FIG. 1 is disclosed in the U.S. patent application Ser. No. 727,153 filed Apr. 25, 1984, abandoned, and assigned to the same assignee as the present application. In the system of FIG. 1, "0" and "1" are identified according to the length of the interval between successive pluses. For instance, the shorter time interval (41 in FIG. 1) between a rising edge of a first pulse and a rising edge of a succeeding pulse denotes "0" while the longer time internal (42 in FIG. 1) between the rising edges of the two successive pulses denotes "1". A certain number of bits consisting of "0"s and "1"s as denoted by different time intervals form a "word", as shown in FIG. 2. In FIG. 2, each word is formed of 6 bits. Various words are used to define instructions.
The above-described system has a drawback in that the time length required for transmitting each word is varied depending on the number of "0"s or "1"s. At the receiving end, the time length of each word is therefore unknown until the end of the transmission of each word. This makes the decoding difficult.
Moreover, the system is easily affected by noises. For instance, when a noise 61 enters during a time interval for "1" as shown in FIG. 4, this will be decoded, at the receiving end, as "00". Such a misinterpretation causes an erroneous operation, which is undesirable in a remote control system.